clean up an outdated comment
bugfix on TCP IPV6_V6ONLY error message output
Ignore bind(2) EADDRNOTAVAIL failure when using getifaddrs()

When no explicit listen addr config is given and the code defaults
  to scanning all available interfaces via getifaddrs(), if the
  bind() operation fails with EADDRNOTAVAIL, we should ignore it
  and move on instead of failing startup.  Apparently some host
  configurations can act this way due to e.g. half-working but
  disabled IPv6 support.
Fixes #30